Various protection mechanisms for lithium ion batteries exist. If a lithium ion battery overcharges, strong exothermic reactions are possible and the potential for causing a fire increases. To prevent a lithium ion battery from overcharging, a battery protection circuit is used. The battery protection circuit, an example of which is shown in FIG. 1, often contains, among other components, a dual channel mosfet 21 with two FET (field effect transistor) switches 22, 24 and a control IC (integrated circuit) 20. One FET prevents current from flowing into the battery, while the other prevents current from flowing from the battery unless the control IC enables it.
Multi-chip modules containing control ICs and MOSFETs exist. However, a number of improvements could be made. For example, some conventional multi-chip modules contain leads on all four sides of the packages. This results in larger modules, which is undesirable, because such modules are used in small electronic devices such as cell phones. The sizes of the multi-chip modules can be reduced, but this reduces the current carrying capacity of the chips that can be used in such packages.
See, for example, U.S. Pat. No. 7,868,432 which is assigned to the same assignee as this patent and is hereby incorporated by reference. It discloses features that lead to a compact, multi-chip module. First, the die mounting pad of the leadframe structure for the power MOSFETs can extend completely from one edge of the multi-chip module to the other. This allows a large size of a power chip on the die mounting pad thereby increasing the current rating of the power MOSFETs. Second, there are no “down bonds” from either the power chip or the IC chip to the leadframe structure. Third, connections between the IC and the power MOSFETs are made by chip-to-chip interconnects (e.g., wire interconnects). Fourth, the number of external leads and signal routing elements adjacent to the MOSFET die mounting pads are reduced. By reducing the external leads and eliminating “down bonds”, the area inside the package is increased to allow for larger power MOSFETs. The increased size of the power MOSFETs reduces on-resistance which reduces power loss and reduces heating. This ultimately increases the useful energy of the battery.